1. Field of the Invention
The present invention relates to polymer compositions comprising amphiphilic compounds polymerizable into conductive polymers, and, more especially, to polymer particles having molecules of such amphiphilic compounds physically anchored into the surface layers thereof and to the production of electroconductive films therefrom.
2. Description of the Prior Art
It is known to this art to prepare conductive polymers comprising backbone chains of conjugated double bonds by anodic polymerization in the presence of conductive salts, or by chemical polymerization under the influence of oxidizing agents, of heterocyclic compounds containing two conjugated double bonds, such as pyrrole, thiophene or furan and the substituted derivatives thereof. Despite their value, the industrial development of these polymers has been slowed by various disadvantages such as a relative chemical instability, poor mechanical properties and, notably, processing difficulties inherent in their low solubility.
It has proven difficult to determine applications even for the most stable of such polymers, for example the polypyrroles. Various solutions to the problem of the processing of conductive polymers of this type have been reported. Thus, it has been described (cf. R. Yosomiya et al., Makromol. Chem. Rapid. Comm., 7, 697-701 (1986)) to prepare composite electroconductive films by contacting pyrrole vapors with a preformed film of a film-forming polymer (polyvinyl alcohol, polyvinyl chloride, polymethyl methacrylate) containing an oxidizing agent (for example CuCl.sub.2).
Published European Patent Application No. 0,206,414 and U.S. Pat. No. 4,521,450 describe polymerizing pyrrole via chemical route in liquid phase within a porous or absorbent solid such as paper or cellulosic materials, natural or synthetic fibers and thin plastic films (for example polyethylene or polypropylene).
Finally, the anodic or chemical polymerization has been described of monomers containing conjugated double bonds, especially pyrrole and the substituted derivatives thereof, in the presence of particles of convertible polymers containing ionic functional groups, serving as a dopant for the uncharged polymer by providing the counterion required to equilibrate the electrical charges of the conductive polymer; cf. published British Patent Application No. 2,124,635, U.S. Pat. No. 4,552,927, European Patent Applications Nos. 0,160,207 and 0,229,992, published French Patent Application No. 2,616,790, S. J. Jasne et al, Synthetic Metals, 15, 175-182 (1986). In a process of this type, the dopant polymer is generally dispersed in the polymerization mixture and, more particularly, the polymerization is carried out within a dopant polymer latex. Such a process proves particularly advantageous because it results in the formation of polymer particles comprising the dopant convertible polymer associated with the electroconductive polymer. Depending on the circumstances, the dispersions of these particles can be employed directly to produce electroconductive articles by coating and evaporation of the dispersion medium, or else the composite electroconductive particles can be isolated from the dispersion medium by conventional techniques and converted into finished or final shaped articles.
Whatever the process employed, it has been determined that the resulting electroconductive polymers lose a portion of their conductivity gradually over the course of time. This decrease is more or less slow, depending on the nature of the electroconductive polymer and depending on its conductivity level. In the case of polypyrrole, in particular, it has been noted that this decrease in conductivity is proportionately more rapid the higher the conductivity of the electroconductive polymer.